1. Field of the Invention
This invention relates to a rear monitoring device for a vehicle, and more particularly to a rear monitoring device for a vehicle which is adapted to permit a driver of a vehicle such as a car or the like to confirm therethrough that the rear of the vehicle or the area or space behind the vehicle is safe.
2. Description of the Prior Art
In general, the rear of a vehicle such as a car, particularly its lower region, is outside the visual field of a driver in a driver's seat. Accordingly, when a driver backs up a vehicle, it is first necessary for the driver to get out of the vehicle to confirm that the area behind the vehicle is safe. This is highly inconvenient and troublesome to the driver.
Some approaches to such a problem have been proposed in the prior art. One of the approaches is to mount a convex mirror on an upper portion of a rear section of a vehicle. However, this method has an important defect in that it causes noteworthy distortion of the image obtained and highly narrows the visual field because the mirror used is convex. Also, it exhibits further disadvantages, such as causing deterioration of the aesthetic appearance of the vehicle, corrosion of the mirror mounting section of the vehicle, and making it possible to steal the mirror because the mirror is mounted on the exterior of the vehicle.
Another approach is to monitor the area to the rear of the vehicle by means of a radio wave. However, this method not only fails to monitor with high accuracy because it utilizes indirect detection due to reflection of a radio wave, but it also causes many problems, such as failure of the radio wave generator, expenses due to use of the generator, and the like.
A further approach is to utilize image transmission by means of a TV camera and receiver set. This method functions satisfactorily and safely, however, it greatly increases expenses because the receiver set is highly expensive. Also, this method is limited to use by only a specific vehicle, such as a large-sized vehicle or the like, because it is necessary to install a TV camera on the outside of the vehicle and position a TV receiver adjacent to the driver's seat.
In view of the foregoing, the inventor proposed a viewer which is typically disclosed in U.S. Pat. No. 4,688,905 issued on Aug. 25, 1987. The viewer is constructed in a manner such that at least one Fresnel concave lens and one or two reflecting mirrors are arranged in a casing formed with a plurality of see-through openings. However, when the viewer is to be mounted on the rear window glass of a vehicle, it is necessary to set the inclination angle of the window glass within a range of 70.degree. to 90.degree.. As the inclination angle is decreased below 70 degrees, the outer edge of the concave lens causes white turbidity to render an image indistinct. Thus, application of the conventional viewer is limited to a specific vehicle.
Further, the above-described construction of the viewer taught in the U.S. Pat. No. 4,688,905 makes it necessary to install the viewer on the exterior of the vehicle; accordingly, it is necessary to make the viewer waterproof. Also, such a construction causes disadvantages, such as deterioration of the aesthetic appearance of the vehicle, corrosion of the viewer mounting section of the vehicle and making it possible to steal the viewer because the mirror is mounted on the outside of the vehicle.
Furthermore, the arrangement of the conventional viewer on the exterior of the vehicle causes the viewer to hinder the operation of automatically washing a vehicle by an automatic washing apparatus. Also, such an arrangement prevents the smooth operation of the rear window wiper.
Accordingly, it would be highly desirable to develop a rear monitoring device for a vehicle which is capable of being installed in the interior of a vehicle and which can function with high accuracy, have a simple structure and be inexpensive, to thereby eliminate the above-noted disadvantages of the prior art.